diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -2926,8 +2926,7 @@
   bool FoundBase = false;
   if (UseExternalLayout) {
     FoundBase = External.getExternalNVBaseOffset(BaseDecl, BaseOffset);
-    if (FoundBase) {
-      assert(BaseOffset >= Size && "base offset already allocated");
+    if (BaseOffset > Size) {
       Size = BaseOffset;
     }
   }